phenol
0
- Joined
- Oct 30, 2007
- Messages
- 533
- Points
- 18
I had a bunch of 74' CMOS chips (nands, flipflops, counters, decoders,...)lying around and i figured i should put them to good use and build a frequency counter. It has a 1-Hz resolution and a 0.5ppm VCTCXO reference oscillator.
While looking for suitable LED 7-segment displays in the junkbox, i found an ancient VF tube from the late 70s. Powered it up and it worked, 35 yrs later. After 3 minutes of googling around I ordered 20 'new' ones, 60 cents a pop. They came in their original packaging and the date code on them is 1990. These are the USSR-made IV-3A 7-segment tubes.
The thing needs 0.7-1v of heater filament voltage and 15-20v on the grid and individual segments. 74 series only has 5v, so i had to boost the available 5v to 20+ volts and step it down to 0.8v ac for the filaments. The two tasks are performed with a HF transformer with 2 secondaries and a push-pull'ed primary runnin off of 5v. The 8 74hc4511 decoder outputs are then level-shifted to 0-20v. All in all, the array of 8 VF tubes draws two times less current than 8 small LED displays.
The tubes glow with greenish-blue color and as you can see, there is noticeable spread of output flux among different specimen. The difference doesnt look so big in real , though. It's measuring 123.45678MHz in those pics.
While looking for suitable LED 7-segment displays in the junkbox, i found an ancient VF tube from the late 70s. Powered it up and it worked, 35 yrs later. After 3 minutes of googling around I ordered 20 'new' ones, 60 cents a pop. They came in their original packaging and the date code on them is 1990. These are the USSR-made IV-3A 7-segment tubes.
The thing needs 0.7-1v of heater filament voltage and 15-20v on the grid and individual segments. 74 series only has 5v, so i had to boost the available 5v to 20+ volts and step it down to 0.8v ac for the filaments. The two tasks are performed with a HF transformer with 2 secondaries and a push-pull'ed primary runnin off of 5v. The 8 74hc4511 decoder outputs are then level-shifted to 0-20v. All in all, the array of 8 VF tubes draws two times less current than 8 small LED displays.
The tubes glow with greenish-blue color and as you can see, there is noticeable spread of output flux among different specimen. The difference doesnt look so big in real , though. It's measuring 123.45678MHz in those pics.